Hybrid Air Separation Method with Noncryogenic Preliminary Enrichment and Cryogenic Purification Based on a Single Component Gas or Liquid Generator

ABSTRACT

Large quantities of high purity and high pressure nitrogen or oxygen gas are produced using a portable system. A PSA, VSA, TSA, or permeable membrane system cleans the air of water and carbon dioxide, as normally required by the cryogenic distillation cycle, but additionally, a significant amount of the oxygen or nitrogen is also removed, depending on the desired produced gas. The removal of the oxygen or nitrogen before the cryogenic process permits the distillation column to be significantly shorter than would otherwise be required. This in turn reduces the size of the equipment such that it can easily be transported and setup. Additionally, a high pressure liquid pump is used to boost the pressure of the nitrogen or oxygen immediately before it goes through the last pass of the cryogenic heat exchanger where the liquid is vaporized and the incoming gas is cooled.

The present application is related to U.S. Provisional Patent Application Ser. No. 61/074,118, filed on Jun. 19, 2008, which is incorporated herein by reference and to which priority is claimed pursuant to 35 USC 119.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of air separation plants, nitrogen or oxygen generators and high pressure nitrogen or oxygen delivery systems, including (but not limited to) those used for drilling and servicing oil and gas wells.

2. Description of the Prior Art

Many procedures and processes utilized by the oil and gas industry, as well as other industries, require the use of one of the components of air, most often nitrogen or oxygen. The use of one of the gases instead of air itself is dictated by the desired result: if oxidation (corrosion, burning, or explosions) is to be eliminated, then nitrogen is used; for many medical and industrial processes, high purity oxygen is required.

Originally the only way to supply high pressure high purity gas in large quantities to the point of use was by having it supplied as a liquid by industrial gas companies, pumping the liquid up to the pressure required (often to as high as 10,000 or 15,000 psig) and then heating the high pressure liquid to turn it into a high pressure gas for delivery to the process or storage. Although this insures a supply of high purity gas (liquid nitrogen is typically 99.99% to 99.999% pure, liquid oxygen is typically 99.5% to 99.7% pure) at high flow rates and high pressures, there are often logistical issues in having sufficient supplies of liquid nitrogen available and delivered to the point of use. Additionally the cost of the delivered liquid (product cost and delivery costs) and the losses incurred by cooling down the equipment and the boil-off of the storage tanks, make liquid use expensive.

In an effort to address some of these issues, on-site non-cryogenic gas generators are often used. In these generators, gas is made at the point of use by supplying compressed air to a pressure/vacuum and/or temperature swing adsorption (i.e. PSA/VSA/TSA) system or to a permeable membrane system. Nitrogen is typically made available at 95% purity as determined by a measurement of less than 5% oxygen; oxygen is typically made available at 93% purity. This approach is widely used to address the logistical issues involved with using liquid, but the pressures achievable (less than 5000 psig) are limited by the existing gas compression equipment, and purities are limited to no more than 99% for nitrogen and 93% for oxygen. In addition, these non-cryogenic systems can only deliver at best approximately 50% and typically 35% to 45% of the available desired component in the feed flow as a product; the remaining is eliminated as a waste gas.

Another method for supplying nitrogen gas on-site is to use a cryogenic gas plant. This system uses the cryogenic distillation process to make high purity nitrogen, which it delivers as a low pressure gas. The low pressure nitrogen gas then needs to be boosted up to a workable pressure, and the available boosters limit the pressure to around 5000 psig. The height of the distillation equipment required by this process is, by necessity, usually very tall (35 to 40 ft or taller) and difficult to transport and set up.

BRIEF SUMMARY OF THE INVENTION

The illustrated general embodiment of the invention is an air separation plant for generating either high purity nitrogen or oxygen (depending on the internals of the separation and distillation modules) comprising a compressor, cleansing module, initial non-cryogenic separation module, and a cryogenic distillation module.

The cleansing module serves to prepare the compressed air for the enrichment process. The air flow is thoroughly cleaned, mechanical impurities and free water are taken out, and then the air is thermally conditioned to have the temperature optimal to the enrichment process (i.e. 130° F. for the permeable membrane array).

The non-cryogenic separation module serves to enrich the process flow with desired component (final product of the separation) and to strip it from all other undesirable elements (mainly water vapor and carbon dioxide).

The distillation module serves to finalize the separation and make the final product. If the final product should be delivered as high pressure gas, then internally, within the distillation module, the product is pressurized as a liquid, and only then is evaporated in the main heat exchanger.

Enriching of the feed flow to the distillation module with the desired component (oxygen for oxygen generators and nitrogen for nitrogen generators) requires fewer trays inside the distillation column than would be required if non-enriched air would have been supplied to the distillation column. Also the total amount of gas supplied to the distillation column is less than if regular air would have been supplied. The lower flow requires less column cross section resulting in smaller diameter trays. The smaller trays permit closer spacing of the trays. The use of fewer trays spaced closer to each other significantly shortens distillation column, and therefore the overall height of the distillation unit.

The illustrated embodiment also comprises a method of generating high purity one component gas from the air by processing the compressed air in three stages: (1) cleansing the compressed air from free water and mechanical impurities, (2) enriching it with a desired component by one of the non-cryogenic methods known (physical, chemical or physical-chemical) and finally (3) finalizing separation by using a cryogenic fractional distillation module.

While the apparatus and method has or will be described for the sake of grammatical fluidity with functional explanations, it is to be expressly understood that the claims, unless expressly formulated under 35 USC 112, are not to be construed as necessarily limited in any way by the construction of “means” or “steps” limitations, but are to be accorded the full scope of the meaning and equivalents of the definition provided by the claims under the judicial doctrine of equivalents, and in the case where the claims are expressly formulated under 35 USC 112 are to be accorded full statutory equivalents under 35 USC 112. The invention can be better visualized by turning now to the following drawings wherein like elements are referenced by like numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the hybrid cryogenic gas generator with non-cryogenic assist of the illustrated general embodiment.

FIG. 2 is a schematic diagram of the hybrid cryogenic low pressure nitrogen gas generator with non-cryogenic assist of the illustrated general embodiment shown in FIG. 1.

FIG. 3 is a schematic diagram of the hybrid cryogenic high pressure nitrogen gas generator with non-cryogenic assist of the illustrated general embodiment shown in FIG. 1.

FIG. 4 is a schematic diagram of the hybrid cryogenic liquid nitrogen generator with non-cryogenic assist of the illustrated general embodiment shown in FIG. 1.

FIG. 5 is a schematic diagram of the hybrid cryogenic low pressure oxygen gas generator with non-cryogenic assist of the illustrated general embodiment shown in FIG. 1.

FIG. 6 is a schematic diagram of the hybrid cryogenic high pressure oxygen gas generator with non-cryogenic assist of the illustrated general embodiment shown in FIG. 1.

FIG. 7 is a schematic diagram of the hybrid cryogenic liquid oxygen generator with non-cryogenic assist of the illustrated general embodiment shown in FIG. 1.

The invention and its various embodiments can now be better understood by turning to the following detailed description of the preferred embodiments which are presented as illustrated examples of the invention defined in the claims. It is expressly understood that the invention as defined by the claims may be broader than the illustrated embodiments described below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The illustrated general embodiment of the invention shown in FIG. 1 is a method for producing and delivering high purity single component gas such as nitrogen or oxygen at high pressures of up to 15,000 psig using an apparatus with a significantly lower profile of no more than 20 feet of overall height than would otherwise be required. A conventional cryogenic gas plant distillation unit (a.k.a. cold box) is supplemented at the front end by using a separation module with a non-cryogenic enrichment system not only to clean the air of water and carbon dioxide, as is normally required by the cryogenic distillation cycle, but additionally, to significantly enrich the feed flow with the desired component by removing a significant amount of the undesired component. The removal of the undesired component before the cryogenic process located in the distillation module permits the distillation column to be significantly shorter than otherwise would be required. This in turn reduces the height of the equipment such that it can easily be transported and setup.

The current invention comprises six main embodiments, namely a method and apparatus for producing low pressure nitrogen gas, high pressure nitrogen gas, liquid nitrogen, low pressure oxygen gas, high pressure oxygen gas, and liquid oxygen.

One of the preferred embodiments of the invention shown in FIG. 2 is a method and apparatus that combines two technologies into a hybrid system that can deliver high purity nitrogen gas while increasing the portability, compact size, and operational convenience of an on-site non-cryogenic generator.

Another one of the preferred embodiments of the invention as shown in FIG. 3 is a method and apparatus that combines three technologies into a hybrid system that can deliver high purity nitrogen gas at high pressures that are typically only achievable by pumping liquid nitrogen from delivered liquid, while increasing the portability, compact size, and operational convenience of an on-site non-cryogenic generator.

In yet another one of the preferred embodiments of the invention as shown in FIG. 4 is a method and apparatus that combines two technologies into a hybrid system that can deliver high purity liquid nitrogen that is available through the cryogenic process, while improving the portability, compact size, and operational convenience of an on-site non-cryogenic generator which cannot produce liquid.

In still another one of the preferred embodiments of the invention as shown in FIG. 5 is a method and apparatus that combines two technologies into a hybrid system that can deliver high purity oxygen gas while improving the portability, compact size, and operational convenience of an on-site non-cryogenic generator.

In yet another one of the preferred embodiments of the invention as shown in FIG. 6 is a method and apparatus that combines three technologies into a hybrid system that can deliver high purity oxygen gas at high pressures that are typically only achievable by pumping liquid oxygen from delivered liquid while improving the portability, compact size, and operational convenience of an on-site non-cryogenic generator.

Finally, in another one of the preferred embodiments of the invention as shown in FIG. 7 is a method and apparatus that combines two technologies into a hybrid system that can deliver high purity liquid oxygen that is available through the cryogenic process while improving the portability, compact size, and operational convenience of an on-site non-cryogenic generator which cannot produce liquid.

All the illustrated embodiments of the invention depicted in FIGS. 2-7 include a diesel or electric drive or engine 1 that drives an air compressor 2, which pressurizes the air to 200 to 500 psig. The pressurized air is then passed through a cleansing module 3, which comprises of at least an air-to-air heat exchanger 31, where it is cooled to near ambient temperatures; a centrifugal separator 32 to remove free water; a particulate filter 33 that removes particles and condensates down typically down to 3 microns; a coalescing filter 34, which removes any remaining fine oil vapor and further condensates from the air, typically down to 0.5 microns or less; an activated carbon bed 35 which removes any remaining hydrocarbons and other contaminants; and a reheater 37 for the purpose of insuring that the moisture remaining in the still saturated air remains in the vapor stage and does not condense on the piping or in any other component of the apparatus. Alternatively, a water-to-air heat exchanger may be used in place of the air-to-air heat exchanger 31.

The cleaned and prepared compressed air is then directed to a separation module 4 comprising a temperature swing absorption system (TSA), a pressure swing absorption system (PSA), a vacuum swing absorption system (VSA), a permeable membrane array, or a combination of aforementioned technologies which is tuned or arranged and configured to remove all remaining water and carbon dioxide from the cleaned air, typically to less than 5 ppm water and less than 15 ppm carbon dioxide. The undesired component is also partially removed as a waste gas although the separation module 4 is not optimized for removal of the undesired component. The separation module 4 is better used for enrichment of the flow with the desired component.

The cleaned enriched air is fed to cold box 5, which comprises a heat exchanger 51, where the enriched air is cooled by the exiting waste gas and the high purity product, the enriched air is then expanded in the turbo expander 52.

In the nitrogen embodiments depicted in FIGS. 2-4, the enriched air from the turbo-expander 52 is then delivered to a distillation column 53 where final separation to the desired purity of the nitrogen is achieved and to a evaporator-reboiler 55. The evaporator-reboiler 55 is used to liquefy the gaseous nitrogen which then irrigates the distillation column 53.

In the oxygen embodiments of the invention depicted in FIGS. 5-7, the enriched air from the turbo-expander 52 is then delivered to the bottom of the evaporator-reboiler 55 where it is liquefied. The liquid air is then throttled into the top of the distillation column 53 for final separation. Liquid oxygen collects in the top of evaporator-reboiler 55 where some evaporates to generate a gas flow up through distillation column 53.

In the nitrogen system embodiments of FIGS. 2-4, waste gas from the top of the evaporator-reboiler 55, or in the corresponding oxygen system embodiments of FIGS. 5-7, waste gas from the top of the distillation column 53, is sent back to the heat exchanger 51 where it is heated by absorbing heat from the incoming enriched feed air as disclosed above and is then released to the atmosphere.

In the low pressure product embodiments for nitrogen in FIG. 2 and oxygen in FIG. 5, the product from the distillation column 53 is forwarded to the heat exchanger 51 in a separate passage than the waste gas where it is heated by absorbing heat from the enriched feed air as disclosed above and is then forwarded to the final application.

For generating high pressure production gas, namely for the nitrogen embodiment in FIG. 3 and the oxygen embodiment in FIG. 6, the liquid product is pressurized to the desired level by a cryogenic pump 56 which is integral to the cold box 5. The high pressure liquid then goes to a high pressure version of heat exchanger 51 for vaporization and cooling of the incoming enriched feed air. The high pressure gas that is produced is then forwarded to the final application.

For applications requiring the product to be in a liquid state, namely nitrogen depicted in FIG. 4 and oxygen depicted in FIG. 7, the purified product can be taken from the distillation column 53, bypassing the heat exchanger 51 and forwarded to the customer for usage or storage.

In the nitrogen embodiments of the invention shown in FIGS. 2-4, the PSA or TSA process normally used at the front of a cryogenic distillation process is replaced with a permeable membrane array 4 that is selected for its ability to remove water and carbon dioxide, and incidentally, 50% to 75% of the oxygen. The dry, oxygen-depleted air stream requires a much smaller heat exchanger 51 to liquefy and smaller distillation column 53 to achieve the high purity (99.99%˜99.999% by volume) nitrogen desired. This smaller heat exchanger 51 and distillation column 53 make the overall system much smaller and easier to transport and setup as compared to a conventional cryogenic gas plant. For example, the entire system 10 can be installed in a conventional 20 foot shipping container, laying distillation column 53 lengthwise in the container, and then upending the container for operation.

Another aspect of the present invention is the capability of delivering very high pressures, such as are typically only achieved in a liquid nitrogen or liquid oxygen pumping system. A standard cryogenic gas plant design takes the low pressure liquid nitrogen or oxygen that comes off the distillation column and passes it through a heat exchanger counter-flow with the incoming air. This serves to warm the newly generated nitrogen or oxygen and starts to cool the incoming air, recovering a significant portion of the refrigeration. The present invention places a high pressure liquid pump 56 in the circuit before the last pass through the heat exchanger 51 in FIGS. 3 and 6. This pump 56 raises the pressure of the liquid as high as 10,000 to 15,000 psig. Such high pressures are not achievable in a conventional on-site PSA or membrane based nitrogen or oxygen generation system. The high pressure liquid is then vaporized in the special high pressure version of heat exchanger 51 designed for this purpose.

In summary, the illustrated embodiment of the invention includes an apparatus for high purity extraction of a selected component from air comprising: a source of air; a cleaning module arranged coupled to the source of air and configured to preferentially remove carbon dioxide and water from the air; a non-cryogenic enrichment module coupled to the cleaning module to preferentially extract the selected component to produce a cleaned modified air mixture enriched in the selected component; and a liquefaction-distillation unit coupled to the enrichment module for liquefying the air mixture enriched in the selected component and separating the selected component from the modified air mixture to provide high purity liquid phase extraction of the selected component. Due to the enrichment before distillation, the liquefaction-distillation unit may thus comprise a shortened liquefaction-distillation column, which can be advantageous operated on a portable or moving platform, ship or vehicle. The selected component is nitrogen or oxygen.

More specifically, the illustrated embodiment includes a nitrogen plant for generating high purity nitrogen to an application comprising: a source of air including nitrogen and oxygen; a non-cryogenic separation module coupled to the source of air, the separation module arranged and configured to preferentially remove carbon dioxide and water from the air but also a portion of the oxygen; and a liquefaction-distillation unit coupled to the separation module for liquefying the nitrogen rich air produced by the non-cryogenic separation module and separating the oxygen from the nitrogen to produce high purity liquid nitrogen.

The plant further comprises a heat exchanger coupled to the liquefaction-distillation unit for vaporizing the high purity liquid nitrogen into a low pressure nitrogen gas.

The plant further comprises a pump coupled between the liquefaction-distillation unit and the heat exchanger for pressurizing the produced high purity liquid nitrogen wherein the heat exchanger is a high pressure heat exchanger, and wherein the liquid nitrogen output from the liquefaction-distillation unit is pumped at high pressure by the pump through the high pressure heat exchanger to deliver high pressure nitrogen gas from the high pressure heat exchanger.

The plant further comprises a multiple stage feed air preparation unit coupled between the source of air and the separation module to clean the air for delivery to the separation module.

The separation module in one embodiment is a molecular sieve type non-cryogenic gas separation system selected for its ability to remove water and carbon dioxide and oxygen from the air.

The separation module in another embodiment is a membrane array selected for its ability to remove water and carbon dioxide and oxygen from the air.

The illustrated embodiment of the invention also includes a method for high purity extraction of a selected component from air comprising the steps of preferentially removing carbon dioxide and water from air to provide cleaned air, non-cryogenically enriching the cleaned air in the selected component; to provide an enriched modified air mixture, liquefying enriched modified air mixture, and fractionally distilling the liquefied modified air mixture to preferentially extract the selected component at high purity in liquid phase. Again due to the step of enriching before fractionally distilling, the fractional distillation may be performed in a shortened column or over a shorter vertical distance, which is an advantage when performed on a portable or moving platform, ship or vehicle. The step of fractionally distilling the liquefied modified air mixture to preferentially extract the selected component at high purity in liquid phase comprises producing high purity liquid nitrogen or oxygen.

The illustrated embodiment of the invention thus also includes a method for generating high purity nitrogen to an application comprising the steps of providing a flow of air, removing carbon dioxide, water, and a portion of the oxygen from the compressed air to form a nitrogen rich gas, liquefying the nitrogen rich gas, and separating the remaining oxygen from the nitrogen rich liquid in a fractional distillation column to produce a high purity liquid nitrogen.

The method further comprises vaporizing the high purity liquid nitrogen in a heat exchanger to produce a high purity low pressure nitrogen gas.

The method further comprises pressurizing of the high purity liquid nitrogen and vaporizing the high purity high pressure liquid nitrogen in a high pressure heat exchanger to produce a high purity high pressure nitrogen gas.

The method further comprises cleaning the air prior to removing carbon dioxide, water, and a portion of the oxygen from the flow of air.

The illustrated embodiment of the invention thus also includes an oxygen plant for generating high purity oxygen to an application comprising: a source of air including nitrogen and oxygen; a non-cryogenic separation module coupled to the source of air, the separation module arranged and configured to preferentially remove carbon dioxide and water from the air but also a portion of the nitrogen; a liquefaction-distillation unit coupled to the non-cryogenic separation module for liquefying the oxygen rich air produced by the non-cryogenic separation module and separating the nitrogen from the oxygen to produce high purity liquid oxygen.

The plant further comprises a heat exchanger coupled to the liquefaction-distillation unit for vaporizing the high purity liquid oxygen into a low pressure oxygen gas.

The plant further comprises a pump coupled between the liquefaction-distillation unit and the heat exchanger for pressurizing the produced high purity liquid oxygen wherein the heat exchanger is a high pressure heat exchanger and wherein the liquid oxygen output from the liquefaction-distillation unit is pumped to a high pressure by the pump through the high pressure heat exchanger to deliver high pressure oxygen gas from the high pressure heat exchanger.

The plant further comprises a multiple stage feed air preparation unit coupled between the source of air and the separation module to clean the air for delivery to the separation module.

The separation module in one embodiment is a molecular sieve type non-cryogenic gas separation system selected for its ability to remove water, carbon dioxide and nitrogen from the air.

The illustrated embodiment of the invention thus also includes a method for generating high purity oxygen to an application comprising the steps of providing a flow of air, removing carbon dioxide, water, and a portion of the nitrogen from the compressed air to form a oxygen rich gas, liquefying the oxygen rich gas, and separating the remaining nitrogen from the oxygen rich liquid in a fractional distillation column to produce a high purity liquid oxygen.

The method further comprises vaporizing the high purity liquid oxygen in a heat exchanger to produce a high purity low pressure oxygen gas.

The method further comprises pressurizing of the high purity liquid oxygen and vaporizing the high purity high pressure liquid oxygen in a high pressure heat exchanger to produce a high purity high pressure oxygen gas.

The method further comprises cleaning the air prior to removing carbon dioxide, water, and apportion of the nitrogen from the flow of air.

Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiment has been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following invention and its various embodiments.

Therefore, it must be understood that the illustrated embodiments have been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following claims. For example, notwithstanding the fact that the elements of a claim are set forth below in a certain combination, it must be expressly understood that the invention includes other combinations of fewer, more or different elements, which are disclosed in above even when not initially claimed in such combinations. A teaching that two elements are combined in a claimed combination is further to be understood as also allowing for a claimed combination in which the two elements are not combined with each other, but may be used alone or combined in other combinations. The excision of any disclosed element of the invention is explicitly contemplated as within the scope of the invention.

The words used in this specification to describe the invention and its various embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definition in this specification structure, material or acts beyond the scope of the commonly defined meanings. Thus if an element can be understood in the context of this specification as including more than one meaning, then its use in a claim must be understood as being generic to all possible meanings supported by the specification and by the word itself.

The definitions of the words or elements of the following claims are, therefore, defined in this specification to include not only the combination of elements which are literally set forth, but all equivalent structure, material or acts for performing substantially the same function in substantially the same way to obtain substantially the same result. In this sense it is therefore contemplated that an equivalent substitution of two or more elements may be made for any one of the elements in the claims below or that a single element may be substituted for two or more elements in a claim. Although elements may be described above as acting in certain combinations and even initially claimed as such, it is to be expressly understood that one or more elements from a claimed combination can in some cases be excised from the combination and that the claimed combination may be directed to a subcombination or variation of a subcombination.

Insubstantial changes from the claimed subject matter as viewed by a person with ordinary skill in the art, now known or later devised, are expressly contemplated as being equivalently within the scope of the claims. Therefore, obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements.

The claims are thus to be understood to include what specifically illustrated and described above, what is conceptionally equivalent, what can be obviously substituted and also what essentially incorporates the essential idea of the invention. 

1. A height-optimized apparatus for high purity extraction of nitrogen from air comprising: a source of compressed air; a non-cryogenic separation module coupled to the source of compressed air to preferentially extract a portion of the oxygen to produce an air mixture enriched in nitrogen; and a cryogenic fractional distillation module coupled to the non-cryogenic separation module for liquefying the air mixture enriched in nitrogen and further separating the nitrogen from the air mixture enriched in nitrogen to provide high purity liquid phase extraction of the nitrogen. 2.-4. (canceled)
 5. The apparatus of claim 1 further comprising a heat exchanger coupled to the cryogenic fractional distillation module for vaporizing the high purity liquid nitrogen into a nitrogen gas.
 6. The apparatus of claim 5 further comprising a pump coupled between the cryogenic fractional distillation module and the heat exchanger for pressurizing the produced high purity liquid nitrogen wherein the heat exchanger is a cryogenic fractional distillation module is pumped at high pressure by the pump through the high pressure heat exchanger to deliver high pressure nitrogen gas from the high pressure heat exchanger.
 7. The apparatus of claim 1 further comprising a multiple stage feed air preparation unit coupled between the source of air and the non-cryogenic separation module to clean the air for delivery to the non-cryogenic separation module.
 8. The apparatus of claim 1 where the non-cryogenic separation module is a molecular sieve type selected for its ability to remove oxygen, water, and carbon dioxide from the air.
 9. The apparatus of claim 1 where the non-cryogenic separation module is a permeable membrane array selected for its ability to remove oxygen, water, and carbon dioxide from the air. 10.-13. (canceled)
 14. A method for generating high purity nitrogen to an application comprising: providing a flow of air; removing carbon dioxide and water to provide a cleaned flow of air; removing a portion of the oxygen from the cleaned flow of air to form a nitrogen rich gas; liquefying the nitrogen rich gas; and separating the remaining oxygen from the nitrogen rich liquid in a fractional distillation column to produce a high purity liquid nitrogen.
 15. The method of claim 14 further comprising vaporizing the high purity liquid nitrogen in a heat exchanger to produce a high purity low pressure nitrogen gas.
 16. The method of claim 15 further comprising pressurizing of the high purity liquid nitrogen and vaporizing the high purity high pressure liquid nitrogen in a high pressure heat exchanger to produce a high purity high pressure nitrogen gas.
 17. The method of claim 14 further comprising cleaning the air prior to removing carbon dioxide, water, and a portion of the oxygen from the flow of air. 18.-26. (canceled) 